1. Field of the Invention
The present invention relates to heated grates for fireplaces and more particularly to hollow heated grates and means for the forced circulation of air through the heated grates.
2. Description of the Prior Art
Hollow heated grates for fireplaces are generally classified in Class 126, subclass 121 under hot air fireplaces. Most manufacturers of forced air hollow grate hot air fireplaces have found it necessary to place the electric motor and blower outside of the fireplace enclosure to avoid overheating the windings of the electric motor. It is not desirable to heat an ordinary commercial electric motor above 140.degree. F. because an increase in temperature will cause rapid deterioration of the insulation and the organic components in the electric motor. Further, when the electric motor windings are heated above 140.degree. F. the resistance of the electrical windings increase which causes an additional heat build-up in the electric windings which rapidly deteriorates the useful life of the motor.
The applicant has marketed an advanced hot air fireplace grate since 1978 which had an electric motor located inside of the fireplace enclosure. The present invention is directed to an improvement of the plenum and enclosure for the electric motor and blower which may be operated inside the fireplace enclosure without exceeding the recommended temperatures of the windings and bearings of the electric motor and blower.
While the plenum enclosure for prior art electric motors was successful in avoiding the heat-build-up in the motor windings when the electric motor was running there was not adequate protection for the electric motor and bearings of the blower when the user inadvertently turned off the power to the electric motor or there was a power failure while the hot air fireplace was being used.
The above mentioned problem often arises in the spring and fall when the user of a hot air fireplace desires the aesthetic environment of a fire without the necessity for the additional heat of a forced air hollow grate hot air fireplace. To avoid this problem the applicants have employed temperature sensing switches on the plenum which holds the electric motor and blower. The switches are always connected to a source of power to turn on the electricity to the motor and blower when the temperature of the plenum reached a temperature approximately 110.degree. F. This temperature sensing switch solved the problem of the user inadvertently disconnecting the power source of the electric motor which maintained the windings of the electric motor in a cool condition. While this sensing switch would prevent the user from forgetting to turn on the blower to maintain the electric motor cool it can not and did not solve a power failure condition when the hollow grate hot air fireplace is being used. The applicants have suggested that vents could be placed in the plenum which holds the electric motor and blower which would induce the flow of air through the plenum when the electric motor is not running and the plenum is hot. The applicants discovered that there are conditions in which the vents placed in the plenums serve as intakes for ingesting smoke from the fireplace enclosure into the plenum and mixing it with the cool intake air so as to create a condition where smoke is forced back into the area to be heated.
There is an unfulfilled need in the art of hot air fireplaces for providing means for preventing the overheating of the windings of the electric motor and the bearings of the blower without creating a condition which would recirculate smoke into the area which is being heated.